水题 Codeforces Round #304 (Div. 2) A. Soldier and Bananas

 1 /*
 2     水题：ans = (1+2+3+...+n) * k - n，开long long
 3 */
 4 #include <cstdio>
 5 #include <algorithm>
 6 #include <cstring>
 7 #include <cmath>
 8 using namespace std;
 9 
10 typedef long long ll;
11 
12 int main(void)        //Codeforces Round #304 (Div. 2) A. Soldier and Bananas
13 {
14     int k, n, w;
15     while (scanf ("%d%d%d", &k, &n, &w) == 3)
16     {
17         ll sum = (1 + w) * w / 2 * k;
18         if (sum < n)    puts ("0");
19         else    printf ("%I64d\n", sum - n);
20     }
21 
22     return 0;
23 }
24 
25 
26 /*
27 3 17 4
28 */